The feasibility of estimating toxicity of synthetic organic chemicals to activated sludge using surrogate test cultures was evaluated. The commercial culture, Polytox, evaluated in this study yielded consistently reproducible results. Experimentally determined IC50 values for 50 chemicals for Polytox cultures correlated well with activated sludge with r2 = 0.922. Similar agreement was found between IC50 values reported in the literature and those measured for Polytox (r2 = 0.762). Additional comparisons were made between activated sludge and Polytox based on joint toxicity of mixtures of organic chemicals. Excellent correlations were found between the concentrations of the constituents in 8- and 10-component mixtures that jointly caused 50% inhibition of the two microorganisms.

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